Digital receiving devices such as computers and microprocessors or other data receiving or manipulation devices normally have a set number of data input lines. When the field digital devices' data lines exceed the number of data input lines, some sort of selection or switching is necessary. Mechanical switching is cumbersome, slow and unreliable. Electronic switching is available, but speed of switching and errors during switching also present a problem. It is known that field digital devices which have diode-transistor logic (DTL) or transistor-transistor logic (TTL) type outputs can have these outputs hard wired together to produce an AND wired logic. Additional circuitry is still required in order to select and verify which device is producing valid data signals when several devices are hard wired together. The present invention overcomes these problems by allowing a digital receiving device to produce a signal which can select a specific field digital device and then verifying that this device is producing a valid signal.